LED display with patterned pixel landings and printed LEDs

ABSTRACT

Pixel locations in an addressable display are defined by metal landings on a top surface of a flexible substrate, such as by depositing a metal film and etching the film. The substrate surface may be hydrophobic so that the hydrophobic surface is exposed between the metal landings. The substrate has conductive vias that connect the metal landings to traces on a bottom surface of the substrate for connection to addressing circuitry. LED ink is then blanket-printed over the top surface and cured to electrically connect bottom electrodes of the LEDs to the metal landings. LEDs that fall between the landings are ineffective. A dielectric layer is blanket-printed which exposes the top electrodes, and a transparent conductor layer is blanket-printed over the LEDs to connect all LEDs associated with an individual pixel location in parallel. Accordingly, all printed steps can be performed without any alignment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/350,625 filed Nov. 14, 2016, which claims priority to U.S.Provisional Patent Application No. 62/256,517 filed on Nov. 17, 2015,assigned to the present assignee and incorporated by reference.

FIELD OF THE INVENTION

This invention relates to addressable displays and, in particular, to avery thin and flexible display formed of printed microscopic lightemitting diodes (LEDs).

BACKGROUND

It is known by the Applicant's previous work to print a conductor layerover a flexible substrate, followed by printing a monolayer ofmicroscopic vertical LEDs over the conductor layer in the desiredorientation so that, after curing, the bottom electrodes of the LEDsohmically contact the conductor layer. A dielectric layer is thenprinted over the conductor layer, followed by printing a transparentconductor layer to contact the top electrodes of the LEDs and connectthe LEDs in parallel. A layer of phosphor may be optionally printed overthe LEDs to wavelength-convert the LED light. When a sufficient voltageis applied to the conductor layers, the LEDs emit light through thetransparent conductor layer. Further detail of forming a light source byprinting microscopic vertical LEDs, and controlling their orientation ona substrate, can be found in U.S. Pat. No. 8,852,467, entitled, Methodof Manufacturing a Printable Composition of Liquid or Gel Suspension ofDiodes, assigned to the present assignee and incorporated herein byreference.

This same printing technique can be used to print pixels comprisingprinting individual conductive pixel landings, such as by using screenprinting with a mask to print metal ink, followed by printing the LEDsover the pixel landings using a corresponding print mask. Alternatively,the metal pixel pattern can be printed over the printed LEDs using theLED print mask. Flexography can also be used for printing the patterns.Another conductor layer connects all the LEDs in each pixel in parallel,and each pixel can be individually energized using an addressingcircuit. Problems with such a method for forming a display include thedifficulty of achieving precise registration of the metal ink patternand the LED ink pattern, the inherent spreading out of the inks afterprinting, the lower quality of a printed metal layer vs. a conventionalmetal film, the difficulty of providing conductive traces from all thepixels to an addressing circuit, the difficulty in patterning ink for avery large display, and the inability to print small pixels.

Thus, what is needed is a simpler and more precise technique for formingan addressable display using microscopic printed LEDs.

SUMMARY

In one embodiment, a metal landing pixel pattern for LEDs is formed on aflexible substrate for an addressable display. The pixel pattern is notformed by printing but is formed by any suitable method used to patternmetal, such as laminating a thin metal film to the substrate andpatterning the film. Such processes include wet etching, laser etching,lift-off, and other techniques. The metal film may be also formed byevaporation or other deposition techniques. Plating may also be used.Patterning the metal landings can be more precise than printing themetal landings using a conductive ink, and the metal will be of a higherquality. This technique can be performed on a large scale.

For cost, reliability, and other reasons, it is desired to form LEDsover the metal landing pixel pattern using an LED ink printing process.However, patterning the LEDs during the printing process to preciselymatch the existing pixel pattern is very difficult.

Rather than patterning the LEDs during printing in the present process,the LEDs are blanket-printed as a monolayer of LEDs over the entiremetal landing pixel pattern. If the pixels have a spacing greater thanthe diameter of a single LED, the LED's bottom electrode will not shortout the pixels. Only LEDs that directly land on a metal landing can beenergized. Narrow spaces between landings result in very little waste ofLEDs. The spaces may also contain a hydrophobic material, so LED inkprinted in the spaces will be pulled into a pixel location by capillaryaction.

After the LED ink is cured, and the bottom electrodes of the LEDselectrically contact their respective metal landings, a thin dielectriclayer is deposited to encapsulate the sides of the LEDs and expose thetop electrodes, followed by depositing a transparent conductor layerover the tops of the LEDs, so all LEDs on a single metal landing form asingle addressable pixel.

The substrate on which the metal landing pixel pattern is formed may bea thin flexible sheet of PET or PMMA. Alternately, the substrate may berigid. Through-holes are initially formed in the substrate thatcorrespond with the pixel pattern. The through-holes are filled with aconductive material to form vias. For example, if the metal landings areformed by evaporation, the metal fills the holes. Other techniques mayalso be used. The vias electrically connect the metal landings to ametal trace pattern on the back of the substrate leading to addressingcircuitry. Therefore, no area on the front side of the substrate is usedfor addressing the pixels.

For a color display, the LEDs may all emit blue light and a red andgreen phosphor pattern can be printed over certain pixels to createaddressable RGB pixels. Each pixel has a variable number of LEDs, butequal current to each pixel would cause the brightness per pixel to bethe same.

Other embodiments are described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a patterned reflective metal film, forming metallandings in a pixel pattern, over a top surface of a thin flexiblesubstrate.

FIG. 2 illustrates the back surface of the substrate on which is formedthin metal traces leading to each of the metal landings via athrough-hole in the substrate.

FIG. 3 is a cross-sectional view along line 3-3 in FIG. 1 showing LEDsblanket-printed over the entire metal landing pattern and cured, alongwith the bottom traces, conductive vias, top transparent conductorlayer, and phosphor areas for creating red and green pixels.

FIG. 4 illustrates a roll-to-roll process for creating the full coloraddressable display of FIG. 3.

FIG. 5 is a flowchart identifying various steps used to form the displayof FIG. 3.

FIG. 6 illustrates an adhesive mounting structure for an array ofindividual tiles, where each tile is identical and similar to that ofFIGS. 1-3.

FIG. 7 illustrates the back of a single tile showing an on-tile decoderand a pluggable connector for attachment to another connector providedby the mounting structure of FIG. 6.

Elements that are similar or identical in the various figures arelabeled with the same numeral.

DETAILED DESCRIPTION

The GaN-based micro-LEDs used in embodiments of the present inventionare less than a third the diameter of a human hair and less than a tenthas high, rendering them essentially invisible to the naked eye when theLEDs are sparsely spread across a substrate. The sizes of the devicesmay range from about 1-200 microns across. This attribute permitsconstruction of a nearly or partially transparent light-generating layermade with micro-LEDs. The number of micro-LED devices per unit area maybe freely adjusted when applying the micro-LEDs to the substrate. A welldispersed random distribution across the surface can produce nearly anydesirable surface brightness. Lamps well in excess of 10,000 cd/m² havebeen demonstrated by the assignee. The LEDs may be printed as an inkusing screen printing, flexography, or other forms of printing. Furtherdetail of forming a light source by printing microscopic vertical LEDs,and controlling their orientation on a substrate, can be found in U.S.Pat. No. 8,852,467, entitled, Method of Manufacturing a PrintableComposition of Liquid or Gel Suspension of Diodes, assigned to thepresent assignee and incorporated herein by reference.

For a large high definition display of, for example, 3 meters across,having 1920 pixels in the horizontal direction, each pixel can be about1.5 mm across. If the LEDs have a diameter of 50 microns, a practicalmaximum of about 20 LEDs can be in each pixel, although in a practicalembodiment only a few LEDs per pixel are needed for sufficientbrightness. The flexible display may even be billboard size and formedof interconnected tiles for ease of handling, where the pixel size ismuch larger.

FIG. 1 illustrates the front surface of a thin, flexible substrate 10having a reflective metal pattern formed over it creating metal landings12 defining pixel locations. The area of each landing 12 can be any sizedepending on the size of the display and the desired resolution (e.g.,full color, high definition). The areas between the landings 12 may beblack to more effectively optically separate the pixels, or the entiresubstrate may be black. For full HD TV, there may be 1920×1080 fullcolor pixels.

The substrate 10 may be a suitable polymer film, such as polycarbonate,PMMA, or PET, less than 200 microns thick and may be dispensed from aroll. The substrate 10 can be any size, since no vacuum processing isneeded for fabrication of the display, and the processing may beperformed using a conveyor system.

The metal landings 12 may be any suitable metal for attachment to thebottom electrodes of the LEDs, such as aluminum, nickel, gold, silver,copper, or an alloy. In one embodiment, a metal foil is laminated ontothe substrate, or a metal layer is evaporated or otherwise deposited onthe surface. In another embodiment, the landings may be formed of aconductive material that is not a metal. A photoresist may then beapplied and patterned using any suitable means, such asphotolithography. The unwanted metal (between the intended landings) isthen etched away using, for example, a wet etch. A programmed laser mayinstead be used to ablate away the undesired metal portions. Many otherprocesses are known for forming very precise metal patterns down to afew microns precision. The landings 12 may also be plated. Forming themetal landing pattern may use conventional techniques, so isinexpensive. This technique is more precise than printing the metallandings 12 using a conductive ink, due to the constraints of printing apattern and the ink spreading somewhat before curing. The quality of themetal will typically be higher than that of a printed metal.

Prior to forming the metal landing pattern, the substrate 10 is providedwith through-holes, aligned with each metal landing location. Thethrough-holes may be filled in a process separate from the process usedto form the metal landings 12 or filled at the same time that the metallandings 12 are formed, if the metal film is formed by deposition ratherthan lamination. The holes may be formed using a laser, stamping, or byetching. In one embodiment, the holes are filled with a conductive ink,and the ink is then cured.

In one embodiment, the substrate 10 has stamped in it the landing pixelpattern (as an array of holes), and the metal for forming the metallandings 12 is deposited over the substrate 10 and removed from thesurface except within the stamped landing pixel pattern. Therefore, thedeposited metal simultaneously forms the landing pixel pattern and theconductive vias. For example, the metal may be deposited over thesubstrate and into the holes as a liquid and then squeegeed off the topsurface of the substrate, leaving only the metal ink in the holes. Themetal ink is then cured. Any deposited metal may be further plated withanother metal.

As shown in FIG. 2, the back surface of the substrate 10 has metaltraces 16 formed on it using conventional techniques, such as the sametechniques used to form the metal landings 12. The ends of the traces 16contact the vias associated with each metal landing 12. The tracematerial may also form the vias by filling the through-holes. Only a fewof the traces 16 are shown, and there is one trace 16 per landing 12,depending on the addressing scheme. Since the traces 16 are formed onthe back surface of the substrate 10, there is a lot of space to routethe traces 16 irrespective of the pixel locations. The traces 16terminate at an address circuit 18 that applies a voltage to any pixellocation to illuminate that pixel to any brightness level.

The substrate 10 with the metal patterns on both surfaces is thensupplied on a roll to complete the fabrication process, as shown in FIG.4, described later.

An LED ink is prepared for blanket-printing over the entire metallanding 12 pattern.

FIG. 3 is a cross-section of a small portion of the display along theline 3-3 in FIG. 1, showing microscopic LEDs 22 printed over the metallanding 12 pattern.

In one embodiment, an LED wafer, containing many thousands of verticalLEDs, is fabricated with a top metal anode electrode 24 for each LED 22.The bottom metal cathode electrode 26 for each LED is reflective tocause almost all the LED light to escape from the top of the LED 22.There is also some side light, depending on the thickness of the LED 22.The anode and cathode surfaces may be opposite to those shown. Eachvertical LED 22 (VLED) may include standard semiconductor GaN layers,including an n-layer, an active layer (e.g., multi-well layers), and ap-layer. The LED 22 is a heterojunction LED.

The LEDs are completely formed on the wafer, including the anode andcathode metallizations, by using one or more carrier wafers, bonded tothe LED wafer by an adhesive layer, during the processing and removingthe growth substrate to gain access to both LED surfaces formetallization. After the LEDs are formed on the wafer, trenches arephotolithographically defined and etched in the front surface of thewafer around each LED, to a depth equal to the wafer thickness, so thateach LED typically has a diameter of less than 50 microns and athickness of about 2-8 microns, making them essentially invisible to thenaked eye. A preferred shape of each LED is hexagonal. The trench etchexposes the underlying wafer bonding adhesive. The bonding adhesive isthen dissolved in a solution to release the LED dies from the carrierwafer. Singulation may instead be performed by thinning the back surfaceof the wafer until the LEDs are singulated. The LEDs 22 of FIG. 3result, depending on the metallization designs. The microscopic LEDs arethen uniformly infused in a solvent, including a viscosity-modifyingpolymer resin, to form an LED ink for printing, such as screen printingor flexographic printing.

The LEDs may instead be formed using many other techniques and may bemuch larger or smaller.

The LEDs 22 are then blanket-printed as a monolayer over the entiresubstrate 10 area containing the metal landings 12, such as byflexography or by screen printing with a suitable mesh to allow the LEDsto pass through and control the thickness of the layer. Because of thecomparatively low concentration, the LEDs 22 will be printed as a loosemonolayer and be fairly uniformly distributed over the substrate 10surface. Any other suitable deposition process may be used. In theexample of FIG. 3, the top anode electrodes 24 are formed to berelatively tall so that the LEDs 22 orient themselves in the directionshown in FIG. 3 by taking the rotational orientation of least resistancewhen settling on the surface of the substrate 10 and metal landings 12.By proper construction of the top electrode, over 90% of the LEDs 22 canbe oriented with their anodes up. In this instance, the LEDs may bedriven with a DC voltage with little loss of light. It is also possibleto print the LEDs with approximately 50% of them pointed “up” andapproximately 50% pointed “down” and drive them with an AC voltage. Anylight emission in a downward direction may be reflected toward the lightexit window of the display.

The solvent is then evaporated by heat using, for example, an infraredoven. After curing, the bottom electrodes 26 of the LEDs 22 remainattached to the underlying metal landings 12 with a small amount ofresidual resin that was dissolved in the LED ink as a viscositymodifier. The adhesive properties of the resin and the decrease involume of resin underneath the LEDs 22 during curing press the bottomelectrode 26 against the underlying metal landing 12, making ohmiccontact with it.

Note that, since the LED ink is not patterned, some LEDs, such as LED22A, will land between the metal landings 12 so cannot be energized.Since the metal landings 12 can be formed close together, there is verylittle waste of LEDs 22. The space between the landings 12 should begreater than the width of the LEDs 22 to prevent the bottom electrode 26of an LED 22 from shorting two landings together.

In another embodiment, a hydrophobic material may be deposited on thesubstrate 10 between the metal landings 12, where the hydrophobicmaterial causes the LED ink to dewet (or be repelled) off the areasbetween the landings 12. Such hydrophobic material 23 is shown in FIG. 1between the landings 12. Therefore, close to 100% of the LEDs 22 will bedeposited over a metal landing 12. If a hydrophobic material is used,the LED 22A in FIG. 3 would not be present between the landings 12. Suchhydrophobic materials are commercially available for a variety ofsolutions that could be used for the LED ink. The hydrophobic materialmay be printed or formed using photolithography.

In another embodiment, the hydrophobic material is deposited over theentire substrate 10 surface, or the substrate 10 itself is hydrophobic,and the metal landing pattern is deposited over the hydrophobic surfaceand then patterned. Therefore, the hydrophobic material 23 will beself-aligned with the metal landings 12.

The hydrophobic material 23, or another material between the landings12, may be black so as to better optically separate the pixels andreduce cross-talk by any light conduction through the substrate 10.

A transparent dielectric layer 28 is then printed over the surface toencapsulate the LEDs 22 and additionally secure them in position. Theink used in the dielectric layer 28 is designed to pull back or de-wetfrom the upper surface of the LEDs 22 during curing to expose the topanode electrodes 24.

A top transparent conductor layer 30 is then blanket-printed over thedielectric layer 28 and LEDs 22 to electrically contact the topelectrodes 24 and is cured in an oven appropriate for the type oftransparent conductor being used. Examples of a printable transparentconductor include ITO and sintered silver nano-wires. All LEDs 22 withina single pixel are connected in parallel, and the number of LEDs 22 perpixel will vary somewhat. Even if the number of LEDs 22 per pixelvaried, the brightness of each pixel will be the same if the samecurrent is supplied to each pixel. By blanket-printing the LED ink, thedielectric layer 28, and transparent conductor layer 30, there are nomasks used for the printing processes, and all the pixel locations aredefined solely by the metal landings 12. Therefore, there is noalignment of printed patterns required.

Metal bus bars 32 are then printed along opposite edges of thetransparent conductor layer 30 and electrically terminate at anode leads(not shown). These bus bars 32 may be considered to have a verticalorientation if the display is held vertically.

Narrow metal runners (outside the plane of the cross-section of FIG. 3)may then be printed in the horizontal direction between the vertical busbars 32 to reduce the resistance across the transparent conductor layer30. The metal runners may be opaque and be routed over the spacesbetween the metal landings 12 to help optically define the pixellocations. The bus bars 32 will ultimately be connected to a powersource using a connector appropriate for the particular application.

The points of connection between the bus bars 32 and the power sourceleads may be at opposite corners of each bus bar 32 for uniform currentdistribution along each bus bar 32 or may be at multiple points alongeach bus bar 32 to reduce the voltage drop across the bus bar 32, forlarge light sheets, to improve electrical efficiency.

If a suitable voltage differential is applied to the anode and cathodeleads of LEDs 22 in a single pixel, all the LEDs 22 in that pixel withthe proper orientation will be illuminated. Multiple pixels, includingall pixels, can be simultaneously energized, depending on the addressingscheme. The pixels may also be energized by raster scanning usingtime-division multiplexing. Any type of addressing may be used.

FIG. 3 also shows the conductive vias 38 extending through the substrate10 for each metal landing 12. Traces 16 form a conductive path betweenthe vias 38 and an address circuit 18 for energizing LEDs within apixel. Only one of the traces 16 is shown in the cross-section of FIG.3.

In another embodiment, if there is sufficient room between the landings12, all traces 16 may be routed on the top surface of the substrate 10between the landings 12. This approach avoids the need for theconductive vias 38.

FIG. 3 also shows a red or green phosphor 40 deposited over a pixel. Ifthe LEDs 22 are GaN types and emit blue light, red and green phosphorareas enable selected pixels to emit red, green, or blue light for afull color display. An RGB pixel group may be formed by adjacent pixels.There may be multiple pixels of a same color in each RGB pixel group forthe proper color component balance.

All light exits the top of the display as shown by the blue light ray 42and the red or green light ray 44. The light ray 44 is shown beingemitted by a phosphor particle 46. Quantum dots may also be used forwavelength conversion.

A black material may be printed between pixels to reduce cross-talkbetween pixels.

The entire display can be formed to have a thickness less than 1 mm.

FIG. 4 illustrates a roll-to-roll process for forming the display ofFIG. 3, and FIG. 5 is a flowchart identifying steps used in thefabrication process. All steps may be performed under atmosphericconditions to produce a very low-cost display screen.

In step 50 of FIG. 5, a reflective metal landing pixel pattern is formedon a flexible substrate 10 where the substrate 10 may be provided on aroll 52 (FIG. 4). The substrate 10 has through holes filled with aconductive material and a trace pattern on the back surface foraddressing the pixels. A hydrophobic material (relative to the LED ink)may be located between the metal landings 12. The substrate 10 may haveany width.

In steps 54 and 55, the LED ink is blanket-printed, at station 56 inFIG. 5, over the substrate 10 and cured, at station 57, to cause thebottom electrodes of the LEDs to electrically contact the metallandings. In a practical embodiment, there may be 1-10 LEDs per metallanding.

In step 58, a dielectric is deposited at station 60 and cured at station62. The dielectric is formed to encapsulate the sides of the LEDs andexpose the top electrodes.

In step 64, a transparent conductor layer is blanket-deposited over allthe LEDs, at station 66, and cured, at station 68, to connect all theLEDs in each pixel in parallel.

In step 70, red and green phosphor dots are printed over those pixelsthat are to emit red and green light, assuming the LEDs emit blue light,at station 72, and cured, at station 74. In another embodiment, the redand green phosphor dots may be printed on a transparent laminationlayer, with clear “dots” for the blue pixels, and the lamination layeris aligned with the substrate 10 and adhered to it. In anotherembodiment, all the LEDs may emit UV, and blue phosphor dots are used tocreate the blue pixels.

The processed substrate 10 may then be cut or supplied on a take up roll76 for further processing.

Any connectors are then provided to connect to the traces on the backsurface of the substrate 10 for addressing the pixels.

In step 80, the completed display is then connected to an addressingcircuit, receiving signals from an image processor, to supply thedesired voltage/current to the various RGB pixels to create a fullcolor, flexible display of any size, such as billboard size. For verylarge displays, an array of display tiles may be interconnected for easeof handling. The display may be static to display an advertisement, ormay be dynamic, such as for a large display for a stadium.

If desired, light diffusion layers or brightness enhancement layers maybe printed on or laminated on the display's exit surface to modify thelight emission pattern and avoid glare. A protective layer may also beprovided.

For very large displays, such as a freeway billboard size of 14 feet×48feet, it is impractical to form a single large array of pixels using thetechniques described above. Therefore, a scheme is required forenergizing pixels in an array of mid-size tiles to form a unified imagein a large display.

It is also impractical to electrically connect the traces 16 (FIG. 2) onthe back of one tile to the traces on the back of another tile due tothe large number of traces for a tile of, for example, 200×200 pixels.Therefore, it is most practical for each tile in an array of tiles to beindependently powered and addressed. This approach will simplify theinstallation of the tiles and the addressing.

FIGS. 6 and 7 illustrate a viable scheme for forming a large displayusing identical tiles, such as those described with respect to FIGS.1-5.

In the simplified example of FIG. 6, it is assumed that a large displaycan be formed using a 3×6 array of identical tiles. The size of eachtile can be optimized and standardized for a variety of display sizes.Therefore, the user can simply be provided any number of tiles from thetile manufacturer and connect them to form a customized display. Thereis no limit on the size of the display.

A display substrate 90 is provided that may be formed of a number ofsections for simplifying handling and installation. For example, thesubstrate 90 may be formed of sections of plywood, plastic sheets, athin film, etc. The substrate 90 may be an existing billboard supportsurface traditionally used to mount a printed image. The intendedpositions of the tiles are shown by the dashed line grid 92.

The top surface of the substrate 90 or the back surface of each tile 94may be a weak, tacky adhesive. The tile 94 is shown being designated forthe bottom right position on the substrate 90.

FIG. 7 illustrates the back surface of the tile 94, where an on-boardaddressing circuit 18 is connected to the traces 16 (FIG. 2) on the backof the tile 94, and the traces are connected to the various pixels onthe front surface of the tile 94. The address circuit 18 may be a serialdecoder that receives a serial bit stream from a master controller 96(FIG. 6), such as using USB technology. Power can also be separatelysupplied to each tile 94 using standard USB technology, where thestandard USB connector supplies power and the serial data. By mountingthe address circuit 18 directly on the back of the tile 94, where thetile 94 acts like a flexible printed circuit board, the delicate traces16 may be reliably connected to the address circuit 18 terminals duringfabrication of the tiles 94 rather than by the user.

Multiple connectors may be used to supply sufficient power to the LEDsin the pixels. However, since not all pixels may be on at the same time(using time division multiplexing), the power to a single tile 94 at anyone time may be less than 500 mA.

The address circuit 18 will generally be a packaged integrated circuitwith a serial input port and output ports connected to the varioustraces on the back of a tile to individually address any pixel.Additional circuits may be used to address and provide sufficient powerto the pixels, such as controllable current sources and video RAMcircuits.

Each tile 94 has a connector 98, such as one or more USB connectors,that connects to a connector 100 from the substrate 90 for each tileposition. For example, the connector 100 may be a recessed fixedconnector that supplies power (e.g., 5 volts) and the serial addressingdata. Alternately, the connectors 100 may be attached to wires on theback of the substrate 90, where the connectors 100 can be pulled throughholes for connection to the tiles 94 and then pushed back into the holesso that the mounting surface for the tiles 94 remains flat. Each addresscircuit 18 may include a controllable current source, or such currentsources may be separate circuits. Each current source is controlled bythe serial data to supply the proper current to the addressed pixel tocontrol the brightness of that pixel.

All the connectors 100 are routed via wires to the master controller 96that receives data from an image processing unit 102, such as a standardcomputer, for supplying the serial data to each of the connectors 100for creating the unified large image. The master controller 96 receivesthe image data and divides the image into sections to be displayed bythe individual tiles 94. Alternatively, the image processing unit 102may divide the image into sections for each tile 94. The mastercontroller 96 then controls each tile 94 independently to produce thedesired image. All the tiles may simultaneously energize one or morepixels at any suitable frequency to avoid flicker. Due to the large sizeof the display, raster scanning of the entire array of pixels (i.e., onepixel at a time) may not be sufficient to achieve the desired brightnessor avoid flicker. The image data provided to the master controller 96may be generated remotely and transmitted to the system via the Internetor other wireless technique. The master controller 96 may be formed ofvarious ICs on a mother board in a computer.

In another embodiment, the same serial data is sent to every decoder forall the tiles 94, and the decoder determines whether the serial dataapplies to that tile. If the serial data applies to that tile,designated by an address code in the serial data, the decoder will causethe addressed pixel in that tile to be energized. This technique cansimplify with wiring to each tile by the substrate since a bus may beused.

Accordingly, any size display can be created using standard size tilesthat are independently connected and controlled by a master controller.

Although the embodiments have been described as addressable displays,the structure may be used to provide white light illumination, where thecolor temperature may be selected by controlling the currents to thered, green, and blue pixels.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects and, therefore, the appended claims areto encompass within their scope all such changes and modifications asfall within the true spirit and scope of this invention.

What is claimed is:
 1. A display device comprising: a substrate having an array of conductive landings forming pixel locations on a first surface of the substrate, the substrate further having conductive traces electrically connected to associated ones of the conductive landings; inorganic, microscopic light emitting diode (LED) dies printed as an LED ink over the array of conductive landings and over areas between the conductive landings and cured, the LED dies comprising singulated dies having at least an n-type layer, a p-type layer, a top electrode, and a bottom electrode, wherein the bottom electrodes of the LED dies electrically contact an underlying conductive landing, and wherein there is a variable number of LED dies electrically connected to each conductive landing; and a transparent conductor layer overlying the LED dies to electrically contact the top electrodes of the LED dies, wherein the LED dies overlying an individual conductive landing are connected in parallel and are energized by a voltage across the transparent conductor layer and an associated trace connected to the individual conductive landing.
 2. The device of claim 1 further comprising the substrate having conductive through-holes associated with the conductive landings, wherein the conductive traces are formed on a second surface of the substrate electrically connected to associated ones of the conductive landings via the conductive through-holes.
 3. The device of claim 1 further comprising a hydrophobic material between the conductive landings on the first surface of the substrate to repel the LED ink between the conductive landings.
 4. The device of claim 1 further comprising addressing circuitry connected to the traces for selectively energizing pixel locations.
 5. The device of claim 1 wherein some of the LED dies are located between the conductive landings and are not energizable.
 6. The device of claim 1 wherein the LED dies emit blue light, the device further comprising at least red and green wavelength conversion materials over selected pixel locations so as to provide red, green, and blue pixels.
 7. A technique for forming a display system: providing a plurality of identical tiles, each tile including an array of addressable pixels; providing a substrate, the substrate being configured for mounting the tiles on the substrate as an array of tiles; each tile having a decoder mounted on it that receives serial data from a master controller and converts the serial data to power and addressing information to power pixels in each tile; each tile having an associated connector for receiving the serial data from the master controller; providing an image processing system for generating image data that is to be displayed by the tiles; mounting the tiles on the substrate and connecting each of the tiles, via its associated connecter, to the master controller; and addressing and powering the pixels in each of the tiles in accordance with the serial data transmitted by the master controller to the tiles.
 8. A display system: a plurality of identical tiles, each tile including an array of addressable pixels; a substrate on which is mounted the tiles as an array of tiles; a plurality of decoders, each decoder being mounted on an associated tile, wherein each decoder receives serial data from a master controller and converts the serial data to power and addressing information to power pixels in an associated tile; plurality of connectors, each connector being associated with a single tile, wherein each connector receives the serial data for an associated tile from the master controller; and an image processing system for generating image data that is to be displayed by the tiles, wherein the tiles are controlled via the master controller to create a unified image displayed by the array of tiles. 